Re: [PATCH] RDMA/rxe: Reject prefetch of a non-ODP MR

[Norbert Szetei]

On Sep 1, 2026, at 09:56, Leon Romanovsky <leon@xxxxxxxxxx> wrote:
> 
> On Thu, Aug 27, 2026 at 12:51:20PM +0200, Norbert Szetei wrote:
>> rxe_ib_advise_mr_prefetch() and rxe_ib_prefetch_sg_list() look up the MR
>> by lkey and hand it to rxe_odp_do_pagefault_and_lock() without checking
>> that it is an ODP MR. That path runs to_ib_umem_odp() on mr->umem, and
>> for a non-ODP MR mr->umem is a plain struct ib_umem from ib_umem_get(),
>> so the container_of() in to_ib_umem_odp() lands past the end of the
>> object and ib_umem_odp_map_dma_and_lock() reads its ib_umem_odp fields
>> out of bounds.
>> 
>> lookup_mr() validates the lkey, PD, access and state but not the MR
>> type, and IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH is accepted for any MR.
>> 
>>  BUG: KASAN: slab-out-of-bounds in ib_umem_odp_map_dma_and_lock+0x884/0x8a0
>>  Read of size 8 at addr ffff88810a3ebcf0 by task advi/921
>>   ib_umem_odp_map_dma_and_lock+0x884/0x8a0
>>   rxe_ib_advise_mr+0x543/0xad0
>>   ib_uverbs_handler_UVERBS_METHOD_ADVISE_MR+0x446/0x530
>>   ib_uverbs_cmd_verbs+0x2b3c/0x3b20
>>   ib_uverbs_ioctl+0x1e3/0x310
>>  Allocated by task 921:
>>   __ib_umem_get_va+0x13e/0xae0
>>   rxe_mr_init_user+0x2ae/0xb00
>>   rxe_reg_user_mr+0x337/0x510
>>  The buggy address belongs to the object at ffff88810a3ebc80
>>   which belongs to the cache kmalloc-96 of size 96
>> 
>> Reject a non-ODP MR after lookup_mr() in both the synchronous and
>> asynchronous prefetch arms.
>> 
>> Fixes: 3576b0df1588 ("RDMA/rxe: Implement synchronous prefetch for ODP MRs")
>> Cc: stable@xxxxxxxxxxxxxxx
>> Signed-off-by: Norbert Szetei <norbert@xxxxxxxxxxxx>
>> ---
>> drivers/infiniband/sw/rxe/rxe_odp.c | 11 +++++++++++
>> 1 file changed, 11 insertions(+)
>> 
>> diff --git a/drivers/infiniband/sw/rxe/rxe_odp.c b/drivers/infiniband/sw/rxe/rxe_odp.c
>> index e870efa7a0a3..5c9dde3501a0 100644
>> --- a/drivers/infiniband/sw/rxe/rxe_odp.c
>> +++ b/drivers/infiniband/sw/rxe/rxe_odp.c
>> @@ -472,6 +472,11 @@ static int rxe_ib_prefetch_sg_list(struct ib_pd *ibpd,
>> return -EINVAL;
>> }
>> 
>> + if (unlikely(!is_odp_mr(mr))) {
>> + rxe_put(mr);
>> + return -EOPNOTSUPP;
>> + }
> 
> The idea is correct, but the implementation needs some improvement.
> 
> RXE stores the access flags in the MR, including IB_ACCESS_ON_DEMAND,
> which indicates that the MR was created as an ODP MR. lookup_mr()
> should check this flag and perform the lookup accordingly.

Do you mean lookup_mr() should take IB_ACCESS_ON_DEMAND into account, so that
the existing (access & mr->access) != access test rejects the non-ODP MR?

rxe_rereg_user_mr() with IB_MR_REREG_ACCESS assigns mr->access directly, and
IB_ACCESS_ON_DEMAND is part of RXE_ACCESS_SUPPORTED_MR. So userspace can set
that flag on a plain MR after registration, without the umem changing. Am I
missing something there? 

Thanks.

> 
> Thanks.